Interesting thread. I never knew much about Mormons, though I’ve been in an analogous situation to the OP: my brother converted to Mormonism and married a Mormon woman. (I don’t know whether it was a sealing or the other type, I didn’t know enough to know there was more than one type.)
Anyway, none of our family attending the wedding – we weren’t invited to any part of the festivities – so the snubbing could be much worse.
The question that was raised, about why some non-Mormons could find being excluded from the ceremony offensive – it’s the one-sided nature of it, I think. So far as I know, all the other denominations of christians are happy to welcome anyone to their churches as visitors – whether of different christian denominations, believers of completely different religions, non-believers, whatever. Come to our services, come to our ceremonies, come to our Fellowship activities – all are welcome.
When you have grown up with that as your tradition, having the door of a church barred to you can be seen as a slap in the face.
Now I’ve just remembered something from my childhood, that was a similar situation. My family is protestant (evangelical Lutheran, if that matters) and when I was around 12 we moved to a house two door down from the Rabbi of a conservative synagogue. He and his wife invited our family to dinner soon after we moved in, and we had a pleasant meal. Then my parents invited their family to dinner the next week – and the Rabbi explained that he and his family could never come eat in our house. We didn’t keep a kosher house, our food was unclean, and as a Rabbi he couldn’t possibly eat each such food, but they hoped we’d come to eat with them often.
Instant and never-to-be-thawed freeze between our families.
The Rabbi wasn’t trying to be offensive, the reverse I’m sure, but there really isn’t any getting around it. Neighborliness is based on reciprocity, as seeing each other as equals. To my parents the other family had turned from potential friends to people who thought we weren’t ‘good enough’ to be true friends with but who they would be willing to feed out of charity.
Hadn’t thought about that in years.